1. Field
Embodiments of the present application generally relate to an optical-scanning apparatus and/or to an image forming apparatus using the optical-scanning apparatus. For example, they may relate to an optical-scanning apparatus deflecting a beam from a light source with a light deflector, focusing the beam with a scanning-image optical system installed at an optical housing, and scanning a photoconductive photoreceptor with the focused beam as a light spot.
2. Discussion of the Background
Recently, image forming apparatuses such as laser printers and digital copiers using the above-mentioned optical-scanning apparatus have come to be known well. Such an image forming apparatus uses, e.g., a polygon mirror 100 having the planar shape of an equilateral hexagon as shown in FIG. 15. The polygon mirror 100 rotates anticlockwise in the direction of an arrow, and there is a turbulence due to a negative-pressure of air then. The turbulence flings dusts and particulate materials in the air down to a part A behind each of the corners of the polygon mirror 100 to the rotation direction thereof, resulting in contamination of the part A. When the surface of the polygon mirror 100 is contaminated, a reflectance thereof deteriorates resulting in deterioration of image quality.
Japanese Patent No. 3652238 discloses a method of using a part B comparatively less contaminated instead of the part A to perform synchro detection for controlling irradiation timing in the main scanning direction.
Published Unexamined Japanese Patent Application No. 11-218710 discloses a method of discharging the polygon mirror so as not to attract dusts.
However, in the method disclosed in Japanese Patent No. 3652238, the contamination of the polygon mirror is inevitable as time passes, and cleaning or exchange thereof is needed. Further, the method disclosed in Published Unexamined Japanese Patent Application No. 11-218710 is insufficient because of not removing the cause of the contamination, but just attracting fewer dusts.
Because of these reasons, a need exists for an optical-scanning apparatus and an image forming apparatus wherein the contamination of polygon mirror can be largely reduced.